Self-extinguishing catalyst composition with monocarboxylic acid ester internal door and propylene polymerization process

ABSTRACT

A catalyst composition for the polymerization of propylene comprising one or more Ziegler-Natta procatalyst compositions comprising one or more transition metal compounds and one or more monoesters of aromatic carboxylic acid internal electron donors; one or more aluminum containing cocatalysts; and a mixture of two or more different selectivity control agents, said SCA mixture comprising from 98.0 to 99.9 mol percent of one or more esters of one or more aromatic monocarboxylic acids or substituted derivatives thereof, and from 2.0 to 0.1 mol percent of one or more alkoxysilane compounds.

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No.60/505,313, filed Sep. 23, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to stereoselective Ziegler-Natta catalystcompositions for use in the polymerization of propylene having improvedcontrol over polymerization activity and reactor process continuitythrough the use of carefully chosen mixtures of selectivity controlagents. Ziegler-Natta propylene polymerization catalyst compositions arewell known in the art. Typically, these compositions include atransition metal compound, especially a mixed titanium, magnesium andhalide containing compound in combination with an internal electrondonor (referred to as a procatalyst); a co-catalyst, usually anorganoaluminum compound; and a selectivity control agent (SCA). Examplesof such Ziegler-Natta catalyst compositions are shown in: U.S. Pat. No.4,107,413; U.S. Pat. No. 4,115,319; U.S. Pat. No. 4,220,554; U.S. Pat.No. 4,294,721; U.S. Pat. No. 4,330,649; U.S. Pat. No. 4,439,540; U.S.Pat. No. 4,442,276; U.S. Pat. No. 4,460,701; U.S. Pat. No. 4,472,521;U.S. Pat. No. 4,540,679; U.S. Pat. No. 4,547,476; U.S. Pat. No.4,548,915; U.S. Pat. No. 4,562,173; U.S. Pat. No. 4,728,705; U.S. Pat.No. 4,816,433; U.S. Pat. No. 4,829,037; U.S. Pat. No. 4,927,797; U.S.Pat. No. 4,990,479; U.S. Pat. No. 5,028,671; U.S. Pat. No. 5,034,361;U.S. Pat. No. 5,066,737; U.S. Pat. No. 5,066,738; U.S. Pat. No.5,077,357; U.S. Pat. No. 5,082,907; U.S. Pat. No. 5,106,806; U.S. Pat.No. 5,146,028; U.S. Pat. No. 5,151,399; U.S. Pat. No. 5,153,158; U.S.Pat. No. 5,229,342; U.S. Pat. No. 5,247,031; U.S. Pat. No. 5,247,032 andU.S. Pat. No. 5,432,244.

Catalyst compositions designed primarly for the polymerization ofpropylene or mixtures of propylene and ethylene generally include aselectivity control agent in order to affect polymer properties,especially tacticity or stereoregularity of the polymer backbone. As oneindication of the level of tacticity, especially the isotacticity ofpolypropylene, the quantity of such polymer that is soluble in xylene orsimilar liquid that is a non-solvent for the tactic polymer is oftenused. The quantity of polymer that is soluble in xylene is referred toas xylene solubles content or XS. In addition to tacticity control,molecular weight distribution (MWD), melt flow (MY), and otherproperties of the resulting polymer are affected by use of a SCA aswell. It has also been observed that the activity of the catalystcomposition as a function of temperature may be affected by the choiceof SCA. Often however, a SCA which gives desirable control over onepolymer property, is ineffective or detrimental with respect toadditional properties or features. Conversely, an SCA that is effectivein combination with one procatalyst may not be effective when used incombination with a different procatalyst.

It is known that the use of certain alkoxy derivatives of aromaticcarboxylic acid esters, especially ethyl p-ethoxybenzoate (PEEB), incombination with a Ziegler-Natta procatalyst composition containing amonoester of an aromatic monocarboxylic acid, exemplified by ethylbenzoate, results in an inferior catalyst composition possessing loweroverall polymerization activity and polymers having relatively lowisotacticities and increased oligomer contents, all of which aregenerally undesired results.

Disadvantageously however, alkoxysilane SCA's, exemplified bydicyclopentyldimethoxy-silane (DCPDMS), methylcyclohexyldimethoxysilane(MChDMS) and n-propyltrimethoxysilane (NPTMS) when used in combinationwith ethylbenzoate internal electron donor results in catalystcompositions that are not generally self-extinguishing. That is, thesecompositions can give polymerization process control problems,especially sheeting and formation of large polymer chunks due to hard tocontrol temperature excursions allowing polymer particles to formagglomerates. Such catalyst compositions are not “self-extinguishing”.Rather, at moderately higher reaction temperatures, they tend to be moreactive, resulting in difficult to control processes. At temperatureclose to the softening or melting point of the polymer being produced,they still possess considerable activity so that the heat generated fromthe exothermic polymerization reaction can significantly contribute tothe formation of agglomerates. In addition, under conditions of areactor upset or a power outage, the normally fluidized reaction bed ofa gas phase polymerization reactor may settle to the diffuser plate ofthe reactor. In that state, continued polymerization may generateexcessive temperatures, resulting in fusion of the entire reactorcontents into a solid mass which requires opening of the reactor andlaborious effort to remove the polymer mass.

Use of mixtures of SCA's in order to adjust polymer properties is known.Examples of prior art disclosures of catalyst compositions making use ofmixed SCA's, especially mixtures of silane or alkoxysilane SCA'sinclude: U.S. Pat. No. 5,100,981, U.S. Pat. No. 5,192,732, U.S. Pat. No.5,414,063, U.S. Pat. No. 5,432,244, U.S. Pat. No. 5,652,303, U.S. Pat.No. 5,844,046, U.S. Pat. No. 5,849,654, U.S. Pat. No. 5,869,418, U.S.Pat. No. 6,066,702, U.S. Pat. No. 6,087,459, U.S. Pat. No. 6,096,844,U.S. Pat. No. 6,111,039, U.S. Pat. No. 6,127,303, U.S. Pat. No.6,133,385, U.S. Pat. No. 6,147,024, U.S. Pat. No. 6,184,328, U.S. Pat.No. 6,303,698, U.S. Pat. No. 6,337,377, WO 95/21203, WO 99/20663, and WO99/58585. References generally showing mixtures of silanes withmonocarboxylic acid ester internal electron donors or other SCA'sinclude: U.S. Pat. No. 5,432,244, U.S. Pat. No. 5,414,063, JP61/203,105,and EP-A-490,45 1.

Despite the advances occasioned by the foregoing disclosures, thereremains a need in the art to provide an aromatic monocarboxylic acidester internal electron donor containing Ziegler-Natta catalystcomposition for the polymerization of olefins, especially propylene andpropylene containing mixtures, wherein the catalyst composition retainsthe advantages of alkoxysilane SCA containing catalyst compositions withregard to polymer properties, but additionally possesses improvedtemperature/activity properties. Especially desired are suchcompositions that are inherently self-extinguishing with regard tocatalyst activity as a function of temperature, thereby leading toreduced polymer agglomerate formation, improved polymerization processcontrol, and increased immunity to reactor upset or power outages.

SUMMARY OF THE INVENTION

The present invention provides a catalyst composition for thepolymerization of propylene or mixtures of propylene and one or morecopolymerizable comonomers, said catalyst composition comprising one ormore Ziegler-Natta procatalyst compositions comprising one or moretransition metal compounds and one or more monoesters of aromaticcarboxylic acid internal electron donors; one or more aluminumcontaining cocatalysts; and a mixture of two or more differentselectivity control agents, said SCA mixture comprising from 98.0 to99.9 mol percent of one or more esters of one or more aromaticmonocarboxylic acids or substituted derivatives thereof, and from 2.0 to0.1 mol percent of one or more alkoxysilane compounds.

The present invention also provides a method of polymerizing propyleneor mixtures of propylene and one or more copolymerizable comonomersunder polymerization conditions using the previously describedZiegler-Natta catalyst composition comprising said mixture of SCA's.More particularly, the process comprises contacting propylene or amixture of propylene and one or more copolymerizable comonomers underpolymerization conditions at a temperature from 45 to 100° C.,preferably from 55 to 90° C., more preferably 60 to 85° C., with acatalyst composition comprising one or more Ziegler-Natta procatalystcompositions comprising one or more transition metal compounds and oneor more internal electron donors selected from the group consisting ofesters of aromatic monocarboxylic acids; one or more aluminum containingcocatalysts; and a mixture of two or more different selectivity controlagents, said SCA mixture comprising from 98.0 to 99.9 mol percent of oneor more esters of one or more aromatic monocarboxylic acids orsubstituted derivatives thereof, and from 2.0 to 0.1 mol percent of oneor more alkoxysilane compounds.

Highly desirably, the polymerization is conducted under conditions oftemperature and SCA content such that no substantial polymeragglomerates are formed in the polymer product and sheeting or foulingof the reactor surfaces is reduced, and preferably, eliminated.Moreover, the present catalyst composition is substantially inherentlyself-extinguishing.

Although a broad range of compounds are known generally as selectivitycontrol agents, a particular catalyst composition may have a specificcompound or group of compounds with which it is especially compatible.The present invention provides a catalyst composition for thepolymerization of propylene or mixtures of propylene and one or morecopolymerizable comonomers which is especially useful with Ziegler-Nattaprocatalyst compositions formed by halogenation of mixed alkoxide metalcompounds. As a result of the present inventors discovery, it has beenunexpectedly discovered that in the foregoing operating range of mixedSCA's the advantages of using an alkoxysilane in combination with anaromatic monocarboxylic acid ester internal electron donor can belargely retained while simultaneously improving the self-extinguishingproperties of the polymerization catalyst. Additional benefits of theinvention include preparation of polymers having narrowed molecularweight distribution. The invention is particularly suited for use in thepreparation of elastomeric ethylene/propylene (EP) andethylene/propylene/diene (EPDM) copolymers where elevated reactortemperatures can easily lead to sticking and agglomeration of thepolymer particles.

DETAILED DESCRIPTION

All reference to the Periodic Table of the Elements herein shall referto the Periodic Table of the Elements, published and copyrighted by CRCPress, Inc., 2001. Also, any reference to a Group or Groups shall be tothe Group or Groups as reflected in this Periodic Table of the Elementsusing the IUPAC system for numbering groups. For purposes of UnitedStates patent practice, the contents of any patent, patent applicationor publication referenced herein are hereby incorporated by reference intheir entirety herein, especially with respect to the disclosure ofstructures, synthetic techniques and general knowledge in the art. Theterm “aromatic” or “aryl” refers to a polyatomic, cyclic, ring systemcontaining (4δ+2) π-electrons, wherein δ is an integer greater than orequal to 1.

If appearing herein, the term “comprising” and derivatives thereof isnot intended to exclude the presence of any additional component, stepor procedure, whether or not the same is disclosed herein. In order toavoid any doubt, all compositions claimed herein through use of the term“comprising” may include any additional additive, adjuvant, or compound,unless stated to the contrary. In contrast, the term, “consistingessentially of” if appearing herein, excludes from the scope of anysucceeding recitation any other component, step or procedure, exceptingthose that are not essential to operability. The term “consisting of”,if used, excludes any component, step or procedure not specificallydelineated or listed. The term “or”, unless stated otherwise, refers tothe listed members individually as well as in any combination.

Unless stated to the contrary or conventional in the art, all parts andpercents used herein are based on weight. The term“(poly)alkyl-substituted” means optionally more than one alkylsubstituent. The term “mixture” when used with respect to SCA's, meansthe use of two or more SCA components, simultaneously during at least aportion of a polymerization. The individual SCA's may be addedseparately to a reactor or premixed and added to the reactor in the formof the desired mixture. In addition, other components of thepolymerization mixture, including the procatalyst, may be combined withone or more of the SCA's of the mixture, and/or the procatalyst,cocatalyst and a portion of the monomer optionally prepolymerized, priorto addition to the reactor.

The benefits of the invention are obtained by operation in a range oflimited availability of alkoxysilane compound, such that desirablepolymer properties exemplified by melt flow, molecular weightdistribution, and/or xylene solubles content, especially MF, are largelyretained while substantially reducing the polymerization activity of thecatalyst composition at elevated reactor temperatures, especiallyreactor temperatures from 85 to 130° C., preferably from 100 to 120° C.

Catalyst compositions demonstrating substantially decreased activity atelevated temperatures, especially at temperatures greater than 100° C.,more preferably greater than 80° C. compared to a standard temperaturesuch as 67° C., are said to be self-extinguishing. In addition, as apractical standard, if a polymerization process, especially a fluidizedbed, gas-phase polymerization, running at normal processing conditionsis capable of interruption and resulting collapse of the bed withoutadverse consequences with respect to agglomeration of polymer particles,the catalyst composition is said to be self-extinguishing.

A complex calculation may be used to compare catalyst activities whenpolymers having different tacticities (measured as xylene solubles orXS) are prepared. The empirically derived equation used to convertcatalyst activity to that of a standard polymer containing 4 percent XSis:Y₄=Y+31.52−10.31X+0.61X², wherein

Y₄ is normalized activity (kg/g procatalyst) at 4.0 percent XS,

Y is the measured catalyst activity (kg/g procatalyst), and

X is the XS content of the polymer in percent measured by the ¹H NMRtechnique of U.S. Pat. No. 5,539,309.

It is to be understood that the present invention is not limited to theuse of any particular polymerization conditions in practice. In fact,the invention is particularly beneficial when employed under gas phasepolymerization conditions, in as much as control of reaction temperatureand prevention of polymer agglomeration is especially critical in a gasphase polymerization, particular under conditions of a reactor upset orpower outage.

Suitable alkoxysilanes for use in the mixture of SCA's herein arecompounds having the general formula: SiR_(m)(OR′)_(4-m)(I) where Rindependently each occurrence is hydrogen or a hydrocarbyl or an aminogroup optionally substituted with one or more substituents containingone or more Group 14, 15, 16, or 17 heteroatoms, said R containing up to20 atoms not counting hydrogen and halogen; R′ is a C₁₋₂₀ alkyl group;and m is 0, 1, 2 or 3. Preferably, R is C₆₋₁₂ aryl, alkaryl or aralkyl,C₃₋₁₂ cycloalkyl, C₃₋₁₂ branched alkyl, or C₃₋₁₂ cyclic amino group, R′is C₁₋₄ alkyl, and m is 1 or 2. Examples of alkoxysilane selectivitycontrol agents for use herein include: dicyclopentyldimethoxysilane,di-tert-butyldimethoxysilane, methylcyclohexyldimethoxysilane,ethylcyclohexyldimethoxysilane, diphenyldimethoxysilane,diisopropyldimethoxysilane, di-n-propyldimethoxysilane,diisobutyldimethoxysilane, isobutylisopropyldimethoxysilane,di-n-butyldimethoxysilane, cyclopentyltrimethoxysilane,isopropyltrimethoxysilane, n-propyltrimethoxysilane,n-propytriethoxysilane, ethyltriethoxysilane, tetramethoxysilane,tetraethoxysilane, cyclopentylpyrrolidinodimethoxysilane,bis(pyrrolidino)dimethoxysilane, andbis(perhydroisoquinolino)dimethoxysilane. Preferred alkoxysilanes arethose containing two methoxy groups. More preferably, the alkoxysilanescontain at least one isopropyl, isobutyl, or C₅₋₆ cycloalkyl group,especially diisopropylclimethoxysilane, diisobutyldimethoxysilane,isobutylisopropyldimethoxysilane, dicyclopentyldimethoxysilane andmethylcyclohexyldimethoxysilane. The latter two silanes are particularlypreferred alkoxysilanes for use in the present invention.

Suitable esters of aromatic monocarboxylic acids for use in combinationwith the foregoing alkoxysilane compounds in the SCA mixture includeC₁₋₂₀ alkyl or cycloalkyl esters of aromatic monocarboxylic acids.Suitable substituted derivatives thereof include compounds substitutedboth on the aromatic ring(s) or the ester group with one or moresubstituents containing one or more Group 14, 15 16, or 17 heteroatoms.Examples of such substituents include (poly)alkylether, cycloalkylether,arylether, aralkylether, alkylthioether, arylthioether, dialkylamine,diarylamine, diaralkylamine, and trialkylsilane groups. Preferred areC₁₋₂₀ hydrocarbyl esters of benzoic acid wherein the hydrocarbyl groupis unsubstituted or substituted with one or more Group 14, 15, 16, or 17heteroatom containing substituents and C₁₋₂₀(poly)hydrocarbyl etherderivatives thereof, more preferred are C₁₋₄ alkyl benzoates and C₁₋₄ring alkylated derivatives thereof, especially, methyl benzoate, ethylbenzoate, propyl benzoate, methyl p-methoxybenzoate, methylp-ethoxybenzoate, ethyl p-methoxybenzoate, and ethyl p-ethoxybenzoate,and most especially, ethyl benzoate or ethyl p-ethoxybenzoate.

An especially preferred combination of SCA components is a mixture ofethyl p-ethoxy-benzoate and dicyclopentyldimethoxysilane ormethylcyclohexyldimethoxysilane.

Preferred SCA mixtures according to the invention are those comprisingfrom 98.5 to 99.5 mol percent, more preferably from 98.6 to 99.0 molpercent of one or more esters of one or more aromatic monocarboxylicacids or substituted derivatives thereof, and from 1.5 to 0.5 molpercent, more preferably from 1.4 to 1.0 mol percent of one or more ofthe specified alkoxysilane compounds.

If larger quantities of monoester are employed in the SCA mixture, thepolymerization activity and selectivity of the reaction are adverselyaffected. If larger quantities of alkoxysilane are employed, theself-extinguishing properties of the invention are not obtained andincreased reaction temperatures, especially temperatures from 65 to 120°C., preferably 80 to 100° C. cannot be employed without possiblyencountering operational difficulties such as agglomerate formation andloss of self-extinguishing properties.

The total molar quantity of the SCA mixture employed in the presentinvention based on moles of transition metal is desirably from 0.1 to1000, more desirably from 0.5 to 500 and most preferably from 1 to 100.The total molar quantity of cocatalyst employed in the present inventionbased on total moles of SCA mixture is desirably from 0.1 to 1000, moredesirably from 1 to 50 and most preferably from 2 to 30.

One measure of self-extinguishing properties for a catalyst compositionis that the normalized polymerization activity at an elevatedtemperature of the composition should be less than that obtainable at areduced temperature such as 65° C. In addition, the normalizedpolymerization activity of the composition should also be less than thatof a comparable catalyst composition wherein the alkoxysilane alone isemployed in the same total SCA molar amount at the temperature ofinterest.

Ziegler-Natta procatalysts for use in the present invention comprise asolid complex derived from a transition metal compound, for example,titanium-, zirconium-, chromium- or vanadium-hydrocarbyloxides,hydrocarbyls, halides, or mixtures thereof; and a Group 2 metalcompound, especially a magnesium halide.

Any of the conventional Ziegler-Natta, transition metal compoundcontaining procatalysts can be used in the present invention. Theprocatalyst component of a conventional Ziegler-Natta catalystpreferably contains a transition metal compound of the general formulaTrX_(x) where Tr is the transition metal, X is a halogen or a C₁₋₁₀hydrocarboxyl or hydrocarbyl group, and x is the number of such X groupsin the compound in combination with the foregoing Group 2 metalcompound. Preferably, Tr is a Group 4, 5 or 6 metal, more preferably aGroup 4 metal, and most preferably titanium. Preferably, X is chloride,bromide, C₁₋₄ alkoxide or phenoxide, or a mixture thereof, morepreferably chloride.

Illustrative examples of suitable transition metal compounds that may beused to form a Ziegler-Natta procatalyst are TiCl₄, TiCl₃, ZrCl₄, TiBr₄,Ti(OC₂H₅)₃Cl, Zr(OC₂H₅)₃Cl, Ti(OC₂H₅)₃Br, Ti(OC₃H₇)₂Cl₂, Ti(OC₆H₅)₂Cl₂,Zr(OC₂H₅)₂Cl₂, and Ti(OC₂H₅)Cl₃. Mixtures of such transition metalcompounds may be used as well. No restriction on the number oftransition metal compounds is made as long as at least one transitionmetal compound is present. A preferred transition metal compound is atitanium compound.

Examples of suitable Group 2 metal compounds include magnesium halides,dialkoxymagnesiums, alkoxymagnesium halides, magnesium oxyhalides,dialkylmagnesiums, magnesium oxide, magnesium hydroxide, andcarboxylates of magnesium. A most preferred Group 2 metal compound ismagnesium dichloride.

Highly desirably, the procatalysts employed in the invention are derivedfrom magnesium compounds. Examples include anhydrous magnesium chloride,magnesium chloride adducts, magnesium dialkoxides or aryloxides, orcarboxylated magnesium dialkoxides or aryloxides. Preferred compoundsare magnesium di(C₁₋₄)alkoxides, especially diethoxymagnesium.Additionally the procatalysts desirably comprise titanium moieties.Suitable sources of titanium moieties include titanium alkoxides,titanium aryloxides, and/or titanium halides. Preferred compounds usedto prepare the procatalysts comprise one or moremagnesium-di(C₁₋₄)alkoxides, magnesium dihalides, magnesiumalkoxyhalides, or mixtures thereof and one or more titanium tetra(C₁₋₄)alkoxides, titanium tetrahalides, titanium(C₁₋₄)alkoxyhalides, ormixtures thereof.

Various methods of making precursor compounds used to prepare thepresent procatalysts are known in the art. These methods are describedin U.S. Pat. Nos. 5,034,361; 5,082,907; 5,151,399; 5,229,342; 5,106,806;5,146,028; 5,066,737; 5,077,357; 4,442,276; 4,540,679; 4,547,476;4,460,701; 4,816,433; 4,829,037; 4,927,797; 4,990,479; 5,066,738;5,028,671; 5,153,158; 5,247,031; 5,247,032, and elsewhere. In apreferred method, the preparation involves chlorination of the foregoingmixed magnesium compounds, titanium compounds, or mixtures thereof, andmay involve the use of one or more compounds, referred to as “clippingagents”, that aid in forming or solubilizing specific compositions via asolid/solid metathesis. Examples of suitable clipping agents includetrialkyl borates, especially triethyl borate, phenolic compounds,especially cresol, and silanes.

A preferred precursor for use herein is a mixed magnesium/titaniumcompound of the formula Mg_(d)Ti(OR^(e))_(e)X_(f) wherein R^(e) is analiphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms orCOR′ wherein R′ is an aliphatic or aromatic hydrocarbon radical having 1to 14 carbon atoms; each OR^(e) group is the same or different; X isindependently chlorine, bromine or iodine; d is 0.5 to 5, preferably 24,most preferably 3; e is 2-12, preferably 6-10, most preferably 8; and fis 1-10, preferably 1-3, most preferably 2. The precursors are ideallyprepared by controlled precipitation through removal of an alcohol fromthe reaction mixture used in their preparation. An especially desirablereaction medium comprises a mixture of an aromatic liquid, especially achlorinated aromatic compound, most especially chlorobenzene, with analkanol, especially ethanol, and an inorganic chlorinating agent.Suitable inorganic chlorinating agents include chlorine derivatives ofsilicon, aluminum and titanium, especially titanium tetrachloride ortitanium trichloride, most especially titanium tetrachloride. Removal ofthe alkanol from the solution used in the chlorination, results inprecipitation of the solid precursor, having especially desirablemorphology and surface area. Moreover, the resulting precursors areparticularly uniform particle sized and resistant to particle crumblingas well as degradation of the resulting procatalyst.

The precursor is next converted to a solid procatalyst by furtherreaction (halogenation) with an inorganic halide compound, preferably atitanium halide compound, and incorporation of an internal electrondonor. If not already incorporated into the precursor in sufficientquantity, the electron donor may be added separately before, during orafter halogenation. This procedure may be repeated one or more times,optionally in the presence of additional additives or adjuvants, and thefinal solid product washed with an aliphatic solvent. Any method ofmaking, recovering and storing the solid procatalyst is suitable for usein the present invention.

One suitable method for halogenation of the precursor is by reacting theprecursor at an elevated temperature with a tetravalent titanium halide,optionally in the presence of a hydrocarbon or halohydrocarbon diluent.The preferred tetravalent titanium halide is titanium tetrachloride. Theoptional hydrocarbon or halohydrocarbon solvent employed in theproduction of olefin polymerization procatalyst preferably contains upto 12 carbon atoms inclusive, more preferably up to 9 carbon atomsinclusive. Exemplary hydrocarbons include pentane, octane, benzene,toluene, xylene, alkylbenzenes, and decahydronaphthalene. Exemplaryaliphatic halohydrocarbons include methylene chloride, methylenebromide, chloroform, carbon tetrachloride, 1,2-dibromoethane,1,1,2-trichloroethane, trichlorocyclohexane, dichlorofluoromethane andtetrachlorooctane. Exemplary aromatic halohydrocarbons includechlorobenzene, bromobenzene, dichlorobenzenes and chlorotoluenes. Of thealiphatic halohydrocarbons, compounds containing at least two chloridesubstituents are preferred, with carbon tetrachloride and1,1,2-trichloroethane being most preferred. Of the aromatichalohydrocarbons, chlorobenzene and o-chlorotoluene are particularlypreferred.

Suitable Ziegler-Natta procatalysts that may be used in the presentinvention may be prepared substantially according to the teachings ofU.S. Pat. No. 4,927,797; U.S. Pat. No. 4,816,433 and U.S. Pat. No.4,839,321. Desirably, the procatalyst is obtained by (i) suspending adialkoxy magnesium optionally mixed with a titanium tetraalkoxide in anaromatic hydrocarbon or halohydrocarbon that is liquid at normaltemperatures, (ii) contacting the suspension with a titanium halide andfurther (iii) contacting the resulting composition a second time withthe titanium halide, and contacting the mixture with an internalelectron donor sometime during the treatment with the titanium halide in(ii). Internal electron donors for use in the present catalystcomposition to provide tacticity control and catalyst crystallite sizingare aromatic monocarboxylic acid esters or (poly)alkyl ether derivativesthereof, especially C₁₋₄ alkyl esters of benzoic acid, especially ethylbenzoate. The Ziegler-Natta, transition metal catalyst may also includean inert support material, if desired. The support should be an inertsolid which does not adversely alter the catalytic performance of thetransition metal compound. Examples include metal oxides, such asalumina, and metalloid oxides, such as silica.

Ziegler-Natta procatalyst compositions for use herein preferably are inthe form of porous particles or crystallites of a relatively uniformsize and shape, thereby allowing close face-to-face contacting betweenparticles resulting in a relatively high bulk density in both a staticor dynamic (fluidized) state. Although porous, the particles desirablyhave a gross morphology substantially in the shape of spheres,spheriod-oblates, grains, or polyhedrons, preferably polyhedrons having10 or more sides. Desirably the ratio of longest axis to shortest axisof the particles is less than 1.2. The particles generally lack surfaceprotrusions. Desirably, 90 percent of the particles are circumscribableby a sphere having a diameter equal in length to the major axis thereof.Such procatalyst particles are referred to as “morphology controlled”procatalysts. Because morphology controlled catalyst compositionsproduce polymer with high bulk density (suitably greater than or equalto 0.35 g/cm³) and are capable of generating large quantities of heatper unit volume, they are conceptually prone to forming polymer particleagglomerates. The present invention desirably imparts self-extinguishingproperties to the catalyst composition, and accordingly is especiallywell suited for use with morphology controlled catalyst compositions.

Cocatalysts for use with the foregoing Ziegler-Natta catalysts accordingto the invention include organoaluminum compounds, such astrialkylaluminum-, dialkylaluminum hydride-, alkylaluminum dihydride-,dialkylaluminum halide-, alkylaluminumdihalide-, dialkylaluminumalkoxide-, and alkylaluminum dialkoxide-compounds containing from 1-10,preferably 1-6 carbon atoms in each alkyl- or alkoxide-group. Preferredcocatalytsts are C₁₋₄ trialkylaluminum compounds, especiallytriethylaluminum (TEA). The quantity of cocatalyst employed may varywithin wide limits but generally is employed in an amount from 1 to 100moles per mole of transition metal compound in the procatalyst.

One suitable method of practicing a polymerization process according tothe present invention comprises performing the following steps in anyorder or in any combination, or subcombination of individual steps:

a) providing a Ziegler-Natta catalyst composition to a polymerizationreactor;

b) providing an organoaluminum cocatalyst compound to the polymerizationreactor;

c) providing a mixture of SCA's meeting the foregoing requirements tothe polymerization reactor;

d) providing one or more polymerizable monomers including propylene tothe reactor; and

e) extracting polymer product from the reactor.

In another suitable method of operation, the one or more esters of oneor more aromatic monocarboxylic acids or substituted derivatives thereofmay be added to the reactor intermittently as a means of controlling thepolymerization activity in the reactor. In this method of operation, thereactor may be operated normally using only an alkoxysilane SCA and whenconditions conducive to the formation of polymer agglomerates or a runaway reaction are encountered, especially when polymerizationtemperatures exceed 80° C., more especially 100° C., the mixed SCA ofthe present invention may be formed in situ, by addition of the one ormore esters of one or more aromatic monocarboxylic acids or substitutedderivative thereof to the reactor contents for a time sufficient toreduce polymer agglomeration, sheeting, or fouling or to otherwisestabilize the polymerization.

In another suitable method of operation, the procatalyst is treated withthe one or more esters of one or more aromatic monocarboxylic acids orsubstituted derivatives thereof (first SCA component) in the presence ofthe aluminum compound cocatalyst. The resulting composition may bestored and shipped prior to use or used directly in a polymerizationreaction according to the invention by combining the same with one ormore alkoxysilanes (second SCA component), optionally in combinationwith additional quantities of one or more monocarboxylic acid ester(s).In this embodiment, trialkylaluminum compounds are preferredcocatalysts. When used, this results in the procatalyst additionallycomprising one or more esters of one or more aromatic monocarboxylicacids or substituted derivatives thereof and an aluminum alkyl compoundand the catalyst composition is prepared by combining the same with oneor more alkoxysilanes, optionally in combination with additionalquantities of one or more monocarboxylic acid ester(s) and/or one ormore cocatalysts.

In another suitable method of operation, the procatalyst may be treatedwith the alkoxysilane SCA component (second SCA component), optionallyin the presence of an aluminum cocatalyst compound. The resultingcomposition may also be stored and shipped prior to use or used directlyin a polymerization reaction according to the invention wherein only thealkyl ester SCA component (first SCA component) is separately added, oroptionally in combination with additional quantities of one or morealkoxysilane(s). In this embodiment as well, trialkylaluminum compoundsare preferred cocatalysts.

The catalyst composition of the invention may be used in most allcommercially known polymerization processes, including thoseincorporating a pre-polymerization step, whereby a small amount ofmonomer is contacted with the catalyst after the catalyst has beencontacted with the co-catalyst and the selectivity control agent mixtureor individual components thereof. Then, the resulting preactivatedcatalyst stream is introduced into the polymerization reaction zone andcontacted with the remainder of the monomer to be polymerized, andoptionally one or more of the SCA components. When used, this results inthe procatalyst additionally comprising one or more alkoxysilanecompounds and an aluminum alkyl compound and the catalyst composition isprepared by combining the same with one or more esters of one or morearomatic monocarboxylic acids or substituted derivatives thereof,optionally in combination with additional quantities of one or morealkoxysilane compounds and/or one or more cocatalysts.

Suitably, the polymerization is conducted at temperatures from 45 to100° C., more preferably from 60 to 85° C. The foregoing temperaturesare average temperatures of the reaction mixture measured at the reactorwalls. Isolated regions of the reactor may experience localizedtemperatures that exceed the foregoing limits.

Preferred polymerization processes in which the present invention isparticularly suited include gas phase, slurry, solution and bulkpolymerization processes, operating in one or more than one reactor.Suitable gas phase polymerization processes include the use ofcondensing mode as well as super condensing mode wherein gaseouscomponents including added inert low boiling compounds are injected intothe reactor in liquid form for purposes of heat removal. When multiplereactors are employed it is desirable that they operate in series, thatis the effluent from the first reactor is charged to the second reactorand additional monomer or different monomer added to continuepolymerization. Additional catalyst or catalyst components (that isprocatalyst or cocatalyst) may be added, as well as additionalquantities of the SCA mixture, another SCA mixture, or individual SCA'scomprising the present SCA mixture. Highly desirably, the mixture ofSCA's is added to only the first reactor of the series. In anotherpreferred embodiment, the polymerization process, or at least one stepthereof, is a solution or slurry polymerization.

More preferably, the process of the invention is conducted in tworeactors in which two olefins, most preferably, propylene and ethylene,are contacted to prepare a copolymer. In one such process, polypropyleneis prepared in the first reactor and a copolymer of ethylene andpropylene is prepared in the second reactor in the presence of thepolypropylene prepared in the first reactor. Regardless of thepolymerization technique employed, it is understood that the mixture ofSCA's and the catalyst composition to be employed, or at least theprocatalyst component thereof may be contacted in the absence of otherpolymerization components, especially monomer, prior to addition to thereactor.

The following embodiments are provided as specific enablement for theappended claims.

1. A catalyst composition for the polymerization of propylene ormixtures of propylene and one or more copolymerizable comonomers, saidcatalyst composition comprising one or more Ziegler-Natta procatalystcompositions comprising one or more transition metal compounds and oneor more monoesters of aromatic carboxylic acid internal electron donors;one or more aluminum containing cocatalyts; and a mixture of two or moredifferent selectivity control agents, said SCA mixture comprising from98.0 to 99.9 mol percent of one or more esters of one or more aromaticmonocarboxylic acids or substituted derivatives thereof, and from 2.0 to0.1 mol percent of one or more alkoxysilane compounds.

2. The catalyst composition of embodiment 1 wherein the internalelectron donor is ethyl benzoate.

3. The catalyst composition of embodiment 1 wherein the SCA mixturecomprises ethyl p-ethoxybenzoate and an alkoxysilane containing two orthree methoxy groups.

4. The catalyst composition of embodiment 3 wherein the alkoxysilane isdicyclopentyldimethoxysilane or methylcyclohexyldimethoxysilane.

5. A catalyst composition according to embodiment 1 wherein the totalquantity of selectivity control agent employed is limited to provide amolar ratio, based on transition metal, from 1 to 100.

6. A catalyst composition according to any one of embodiments 1-5wherein the SCA mixture comprises from 98.5 to 99.5 mol percent of oneor more alkyl esters of one or more aromatic monocarboxylic acids orsubstituted derivatives thereof, and from 1.5 to 0.5 mol percent of oneor more alkoxysilane compounds

7. A polymerization process comprising contacting propylene or a mixtureof propylene and one or more copolymerizable comonomers underpolymerization conditions at a temperature from 45 to 100° C. with acatalyst composition comprising one or more Ziegler-Natta procatalystcompositions comprising one or more transition metal compounds and oneor more internal electron donors selected from the group consisting ofesters of aromatic monocarboxylic acids; one or more aluminum containingcocatalysts; and a mixture of two or more different selectivity controlagents, said SCA mixture comprising from 98.0 to 99.9 mol percent of oneor more esters of one or more aromatic monocarboxylic acids orsubstituted derivatives thereof, and from 2.0 to 0.1 mol percent of oneor more alkoxysilane compounds.

8. The method of embodiment 7 conducted at a temperature from 60 to 85°C.

9. The method of embodiment 7 wherein the internal electron donor isethyl benzoate.

10. The method of embodiment 7 wherein the SCA mixture comprises ethylp-ethoxybenzoate and a dimethoxysilane.

11. The method of embodiment 7 wherein the alkoxysilane isdicyclopentyldimethoxysilane or methylcyclohexyldimethoxysilane.

12. The method according to any one of embodiments 7-11 conducted undergas phase polymerization conditions.

13. The method according to any one of embodiments 7-11 which isconducted in more than one reactor operating in series.

The invention is further illustrated by the following examples thatshould not be regarded as limiting of the present invention. Unlessstated to the contrary or conventional in the art, all parts andpercents are based on weight.

EXAMPLE 1

A titanium containing Ziegler-Natta catalyst composition is employed toproduce polypropylene homopolymers. The catalyst composition includes aprocatalyst compound prepared by slurrying a mixture of a magnesiumdiethoxide and titanium ethoxide/chloride containing precursorcorresponding to the formula Mg₃Ti(OC₂H₅)₈Cl₂ (made substantiallyaccording to U.S. Pat. No. 5,077,357) with ethyl benzoate (0.10 ml/gramprecursor) in a 50/50 (vol/vol) mixture of TiCl₄/monochlorobenzene (MCB,15.9 ml/gram precursor). After the mixture is heated at 70° C. for 30minutes, it is filtered. The resulting moist mass is slurried in a 50/50TiCl₄/MCB mixture (15.9 ml/gram precursor) and benzoyl chloride (0.056ml/gram precursor) at 99° C. for 10 minutes and filtered. The lastprocess is repeated once with 0.10 ml/gram precursor at 95° C. for 10minutes. The resulting solid is rinsed with isopentane and then driedwith flowing warm nitrogen.

Propylene polymerizations are carried out in a 3.6 L, jacketed, stirredstainless steel reactor. All solvents and the reactor interior are driedprior to use. The reactor conditions employed are: an initial charge of3.0 standard liters H₂, 2.7 liters propylene, 2.5 ml of a 5 percentsolution of triethylaluminum (TEA) in heptane, measured quantities ofSCAs for a total amount of 0.35 mmol (calculated to give a SCA/Ti ratioof 70/1 and a A1/SCA molar ratio of 2.0), and 16.43 mg of theprocatalyst as a 5.0 percent mineral oil slurry. Catalyst components areinjected into reactor at 60° C. Polymerization is conducted at 67° C.for one hour. Upon completion of polymerization, the reactor is ventedto ambient pressure and opened to the atmosphere.

The SCA mixtures tested include: dicyclopentyldimethoxysilane(DCPDMS)/PEEB, methylcyclohexyldiinethoxysilane (MChDMS)/PEEB,diisobutyldimethoxysilane (DiBDMS)/PEEB, and n-propyltrimethoxysilane(NPTMS)/PEEB. Normalized activity (Y₄) for the various SCA combinations,amounts and temperatures are provided in Table 1.

TABLE 1 Polymerization Results Silane/Ester Activity, Y₄ Y₄ increase RunSCA mixture (mol percent) (kg/g procat.) (percent)  1* DCPDMS/PEEB 0/100 22.0  2 ″ 0.5/99.5 28.6 30  3 ″ 1.0/99.0 23.7 8  4 ″ 2.0/98.026.9 20  5* MChDMS/PEEB  0/100 23.7  6 ″ 0.5/99.5 28.6 21  7 ″ 1.0/99.029.4 24  8 ″ 2.0/98.0 29.3 24  9* DiBDMS/PEEB  0/100 25.8 10 ″ 0.5/99.528.7 11 11 ″ 1.0/99.0 27.9 8 12 ″ 2.0/98.0 26.7 4 13* NPTMS/PEEB  0/10023.7 14 ″ 0.5/99.5 21.8 decrease 15 ″ 1.0/99.0 25.6 8 16 ″ 2.0/98.0 26.612 *comparative, not an example of the invention

As may be seen by reference to the results of Table 1, by using certainmixtures of SCA's according to the invention, improved polymerizationactivity (normalized to standard XS content) may be obtained compared touse of the carboxylic acid ester compound alone. The best results areobtained by the use of an SCA mixture containing a silane containing aC₅₋₆ cyclic group.

Moreover, by using certain mixtures of SCA's according to the invention,reduced polymerization activity may be obtained at elevatedpolymerization temperatures, compared to use of the silane SCA compoundalone or compared to the use of the same SCA mixture at a lowerpolymerization temperature. The reduction may be controlled by adjustingthe quantities of silane and secondary SCA employed, so that activitylevels substantially less than those obtainable by use of the silane SCAalone or less than the activity with the same SCA mixture at 67° C. areobtainable. Those illustrated compositions possess self-extinguishingpolymerization properties. Although using larger amount of alkoxysilanemay lead to higher catalyst activity, the self-extinguishing property ofthe catalyst system diminishes with increasing amount of alkoxysilane.For a process that requires high degree of self-extinguishing property,a mixture containing small amount of alkoxysilane is beneficial.Accordingly, use of such SCA mixtures can reduce or avoid anuncontrolled acceleration of the reaction, as well as softening ormelting of polymer particles that leads to agglomerate formation andsheeting or fouling of the reactor.

1. A catalyst composition for the polymerization of propylene ormixtures of propylene and one or more copolymerizable comonomers, saidcatalyst composition comprising one or more Ziegler-Natta procatalystcompositions comprising: one or more transition metal compounds and oneor more monoesters of aromatic carboxylic acid internal electron donors;one or more aluminum containing cocatalyst; and a mixture of two or moredifferent selectivity control agents (SCA), said SCA mixture comprisingfrom 98.5 to 99.9 mol percent of one or more esters of one or morearomatic monocarboxylic acids or substituted derivatives thereof, andfrom 1.5 to 0.1 mol percent of one or more alkoxysilane compounds. 2.The catalyst composition of claim 1 wherein the internal electron donoris ethyl benzoate.
 3. The catalyst composition of claim 1 wherein theSCA mixture comprises ethyl p-ethoxybenzoate and an alkoxysilanecontaining two or three methoxy groups.
 4. The catalyst composition ofclaim 1 wherein the alkoxysilane is dicyclopentyldimethoxysilane ormethylcyclohexyldimethoxysilane.
 5. A catalyst composition according toclaim 1 wherein the total quantity of selectivity control agent employedprovides a molar ratio, based on transition metal, from 1 to
 100. 6. Thecatalyst composition according to claim 1 wherein the SCA mixturecomprises from 98.5 to 99.5 mol percent of one or more alkyl esters ofone or more aromatic monocarboxylic acids or substituted derivativesthereof, and from 1.5 to 0.5 mol percent of one or more alkoxysilanecompounds.
 7. The catalyst composition of claim 1 wherein the SCAmixture comprises from 98.6 to 99.0 mol percent of one or more alkylesters of one or more aromatic monocarboxylic acids or substitutedderivatives thereof, and from 1.4 to 1.0 mol percent of one or morealkoxysilane compounds.
 8. The catalyst composition of claim 1 whereinthe alkoxysilane is selected from the group consisting ofdiisopropyldimethoxysilane, diisobutyldimethoxysilane, andisobutylisopropyldimethoxysilane.
 9. The catalyst composition of claim 1wherein the SCA mixture comprises ethyl p-ethoxybenzoate and analkoxysilane selected from the group consisting ofdicyclopentyldimethoxysilane, methylcyclohexyldimethoxysilane, andn-propyltrimethoxysilane.
 10. The catalyst composition of claim 1wherein the Ziegler-Natta procatalyst composition is a morphologycontrolled procatalyst.
 11. A polymerization method comprising:contacting propylene or a mixture of propylene and one or morecopolymerizable comonomers under polymerization conditions at atemperature from 45 to 100° C. with a catalyst composition comprisingone or more Ziegler-Natta procatalyst compositions comprising one ormore transition metal compounds and one or more internal electron donorsselected from the group consisting of esters of aromatic monocarboxylicacids, one or more aluminum containing cocatalysts; and a mixture of twoor more different selectivity control agents, said SCA mixturecomprising from 98.5 to 99.9 mol percent of one or more esters of one ormore aromatic monocarboxylic acids or substituted derivatives thereof,and from 1.5 to 0.1 mol percent of one or more alkoxysilane compounds.12. The method of claim 11 conducted at a temperature from 60 to 85° C.13. The method of claim 11 wherein the internal electron donor is ethylbenzoate.
 14. The method of claim 11 wherein the SCA mixture comprisesethyl p-ethoxybenzoate and a dimethoxysilane.
 15. The method of claim 11wherein the alkoxysilane is dicyclopentyldimethoxysilane ormethylcyclohexyldimethoxysilane.
 16. The method according to claim 11conducted under gas phase polymerization conditions.
 17. The methodaccording to claim 11 conducted in more than one reactor operating inseries.